Electronic equipment racks generally are designed to receive a number of electronic components arranged vertically in the rack, mounted on shelves, and/or to front and rear mounting rails. The electronic equipment may include, for example, printed circuit boards, communications equipment, computers, including computer servers, or other electronic components.
Electronic equipment housed in racks produces a considerable amount of heat, which undesirably affects performance and reliability of the electronic equipment. Often the heat produced by the rack-mounted components is not evenly distributed in the racks. Temperature gradients causing elevated inlet temperatures at tops of racks, for example, reduce equipment reliability substantially. Equipment reliability may be reduced by as much as half the reliability of specific equipment function for each 10° F. rise in temperature. Accordingly, rack-mounted computer systems typically require effective cooling systems to maintain operational efficiency. Cooling can be accomplished by introducing cooled air into an equipment rack causing the air to flow through equipment in the rack and exit the rack at an increased temperature, thereby removing some of the heat. The heat removed from the rack is typically returned into the room containing the racks and the entire room is cooled using a relatively large air conditioning system.